Denaturation of myofibrillar proteins from chickens as affected by pH, temperature, and adenosine triphosphate...

The susceptibility to denaturation of myofibrillar protein from chicken muscles was investigated and compared with denaturation of myofibrillar protein from pork. Immediately postmortem, the Pectoralis profundus (white muscle) and the Pubo-ishio femorale (red muscle) of six Arbor Acres chickens were collected. The Semimembranosus (white muscle) and Psoas major (red muscle) of three Yorkshire x Landrace and three Yorkshire x Landrace x Duroc pigs were collected at 45 min postmortem. Protein denaturation was prevented by keeping the muscles at 0 to 2 C in a buffer (pH 7.2) containing ethylene glycol-bis (beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) (to sequester Ca ions). After purification, myofibrils were incubated at 25 or 40 C, pH 5.4 or 6.5, with 0, 0.68, or 3.4 mM adenosine triphosphate (ATP). Protein solubility, an indicator of denaturation, was assessed after 0, 10, 20, and 60 min incubation. Protein solubility of chicken pectoralis myofibrils was not affected by any of the conditions. In the other myofibrils, pH 5.4 caused significantly (P < 0.05) more protein denaturation than pH 6.5, and incubation at 40 C resulted in significantly more protein denaturation than incubation at 25 C. The presence of ATP (tested at pH 6.5) affected denaturation; higher ATP concentrations resulted in increased loss of solubility. We concluded that chicken red myofibrillar proteins are equally susceptible to denaturation as are pork red and white myofibrils. Chicken pectoralis (white) muscle fibers are least susceptible to denaturation. The results of this study indicate that factors other than protein denaturation are responsible for the low water-holding capacity of pale, soft, exudative chicken breast muscle.